20.2: The Respiratory System: the exchange of gases

• Section Objectives:• Identify the structures involved in external respiration.

• Contrast external and cellular respiration• Explain the mechanics of breathing.

Why do we need a respiratory system?

• Need O2 in– for cellular respiration– make ATP

• Need CO2 out– waste product

O2

food

ATP

CO2

Passageways and Lungs

• respiratory system consists of a pair of lungs & a system of tubes that carry air to them

• Breathing is just one of the functions that the respiratory system carries out.

The path air takes• air enters through

the nasal cavity – It passes through

the pharynx and larynx into the trachea

– The trachea forks to form two bronchi

– Each bronchus branches into numerous bronchioles

• The bronchioles end in clusters of tiny sacs called alveoli

Lungs• Structure

spongy texture • high surface area• more absorption of O2

– alveoli • small air sacs

– moist lining• mucus traps dust,

pollen, particles– covered by cilia

• hair-like extensions of cells• move mucus upward to

clear out lungs

Moving gases into bloodstream• Inhale

– O2 passes from alveoli to blood

– by diffusion

• Exhale– CO2 passes from blood

to alveoli– by diffusion

capillaries(circulatory system)

Gas exchange: Diffusion of gases• Gases move by diffusion from high to low

concentration– capillaries are thin-walled tubes of circulatory

system– alveoli are thin-walled sacs of respiratory system

blood lungs

CO2

O2

CO2

O2

blood body

CO2

O2

CO2

O2

capillaries in lungs capillaries in muscle

External respiration: exchange of gases between alveoli and blood

Internal respiration: exchange of gases between blood and ce4lls

The Mechanics of Breathing

• Breathing ventilates the lungs• The action of your diaphragm and the muscles between your

ribs enable you to breathe in and breathe out.

• Breathing is the alternation of inhalation (active) and exhalation (passive)

Control of Respiration• Breathing is usually an involuntary

process.

• partially controlled by an internal feedback mechanism that involves signals being sent to the medulla oblongata about the chemistry of your blood.– measure blood pH

• CO2 = pH (acid)– coordinate

breathing, heart rate & body’s need for energy

• will send nerve signals to the rib muscles and diaphragm.

• nerve signals cause these muscles to contract, and you inhale.

Breathing and Homeostasis• Homeostasis

– keeping the internal environment of the body balanced

– need to balance O2 in and CO2 out

– need to balance energy (ATP) production• Exercise

– breathe faster• need more ATP• bring in more O2 & remove more CO2

• Disease– poor lung or heart function = breathe faster

• need to work harder to bring in O2 & remove CO2

O2

ATP

CO2

Cleaning dirty air

• To prevent foreign material from reaching the respiratory system is lined with ciliated cells that secrete mucus.

• The cilia constantly beat upward in the direction of your throat, where foreign material can be swallowed or expelled by coughing or sneezing